Partial purification and characterization of an inducible extracellular β-Glucosidase of Aspergillus niger IMI 502691
β-Glucosidase (EC 188.8.131.52) was produced by Aspergillus niger IMI 502691 using solid state fermentation of cassava root fibre. The enzyme was partially purified and characterized. The enzyme extracted using 20mM phosphate buffer pH 6.8 was concentrated to 10ml with 5M sucrose solution using dialysis membrane. It was purified from the culture medium by ion exchange chromatography on Carboxymethyl Sepharose and gel filtration chromatography on Biogel P 4. β- Glucosidase was purified 3.17 fold to give 3.68% yield relative to the total activity in the crude extract and with over 300% increase in specific activity of 106.93Umg-1 proteins for the partially purified protein. The enzyme exhibited decrease in total protein and total activity of 86.1% and 27.16%, respectively and optimal activity at pH 5.0 and 80oC (1h) in the absence of calcium. The β- glucosidase showed a wide range of pH and temperature of 3.0 to 7.0 and 50oC to 90oC, respectively. The enzyme was most stable at 50oC but retained above 50% of its activity for 1h at 60oC. The β-glucosidase of Aspergillus niger IMI 502691 was significantly activated by Sr2+, Fe2+, Mn2+, Ni2+, Zn2+and Cu2+ tested except for Ca2+ which inhibited the enzyme.
Keywords: Glucosidase, chromatography,extract,activity, inhibited